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Farmall & IHC Tractors Discussion Forum
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Warning Diode for 12v conversion

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Wisconsin_Joe

07-16-2007 21:43:41




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Here goes,

I have been studying Bob's wiring diagrams (which I might add are life savers, thanks Bob) and applying them to the existing 12v conversion om my '43 H. My configuration looks closest to diagram #6 (Farmall Super H/M 12 volt Delco 10-SI alternator conversion). The only thing I notice is there is no wire from the ignition to post# 1 (warning bulb/diode) on the alternator. I just wanted to check with you guys before I move forward and add the diode wire that I am not missing something here. I have been reading the forums on this and I would like to use the (Radio Shack #276-1114)2.5 Amp @ 1000 PIV diode. Finally to my question. Please ignore my ignorance but are diodes uni-directional meaning do they have to be installed in a certain direction or does it not matter. I just don't want to get something installed backwards if I can help it! Thanks again!

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John T

07-17-2007 06:42:02




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 Re: Warning Diode for 12v conversion in reply to Wisconsin_Joe, 07-16-2007 21:43:41  
Joe, The purpose of that "diode" is to prevent the alternator from backfeeding voltage to the coil allowing the tractor to still run even though you turn the ignition OFF. NOTE I recommend a 10 ohm minimum current limiting safety resistor (instead of the diode) where the didoe may not??? even be required but can still easily be added if she wants to run when the ignition is switched OFF. YES its very polarity sensitive cuz it acts sort of an electrical current flow check valve allowing current to flow through it in one direction BUT NOT in reverse. For Neg ground its banded cathode end is towards the alternator.

NOTE Ive seen em work fine with ONLY the diode orrrrr rr with a current limiting safety resistor (like my 10 ohm) or even an idiot light which may be way more then the minumim 10 ohms I recommend. Your tractor your call..... .....

John T

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Owen Aaland

07-17-2007 03:57:20




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 Re: Warning Diode for 12v conversion in reply to Wisconsin_Joe, 07-16-2007 21:43:41  
If this is an existing conversion and it is working without the wire you have a "One Wire" regulator in the alternator. You do not have to add the extra wire but if you do you will notice the alternator will start to charge without reving the engine first. The downside is you have to add a resister or diode or the engine will not shut off with the switch.



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Bob

07-16-2007 22:08:04




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 Re: Warning Diode for 12v conversion in reply to Wisconsin_Joe, 07-16-2007 21:43:41  
I'm "Bob", NOT BobM.

I just looked at BobM's #6 diagram, and there clearly IS a wire from the "run" terminal on the ignition switch, through an "idiot light", to the alternator's #1 "switched excite" terminal.

The diagram is labeled "6 -Farmall Super H/M 12 volt Delco 10-SI alternator conversion". Are we looking at the same diagram?

If you decide to use a diode INSTEAD of an "idiot light", yes, diodes are polarity-sensitive. The cathode end, usually marked by a white band, goes towards the alternator's #1 terminnal, like THIS:

Third Party Image

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Wisconsin_Joe

07-17-2007 06:03:50




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 Re: Warning Diode for 12v conversion in reply to Bob, 07-16-2007 22:08:04  
Thanks for the help! Joe



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K.B.-826

07-16-2007 22:05:50




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 Re: Warning Diode for 12v conversion in reply to Wisconsin_Joe, 07-16-2007 21:43:41  
Yes sir! It does matter which way they are installed. That's the point of the diode- to only allow power to flow one direction. Power should flow from a source of switched 12-volt power (usually the ignition circut), through the diode, and to the #1 terminal to exite the alternator. The diode prevents power from backfeeding from the #1 terminal to the ignition circut, which would cause the engine to run on after the ignition switch is turned off.

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